System and method for identifying a vascular border

ABSTRACT

A system and method is provided for using a first vascular image, or more particularly a plurality of control points located thereon, to identify a border on a second vascular image. Embodiments of the present invention operate in accordance with an intra-vascular ultrasound (IVUS) device and a computing device electrically connected thereto. Specifically, in one embodiment of the present invention, an IVUS console is electrically connected to a computing device and adapted to acquire IVUS data. The IVUS data (or multiple sets thereof) is then provided to (or acquired by) the computing device. In one embodiment of the present invention, the computing device includes a plurality of applications operating thereon—i.e., a border-detection application, an extrapolation application, and an active-contour application. These applications are used to (i) identify a border and control points on a first IVUS image (i.e., any IVUS image), (ii) extrapolate the control points to a second IVUS image (i.e., another IVUS image), (iii) identify a border on the second IVUS image, and (iv) adjust the border on the second IVUS image in accordance with at least one factor. In one embodiment of the present invention, the at least one factor is selected from a group consisting of gradient factor, continuity factor, and curvature factor.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit pursuant to 35 U.S.C. §119(e) of U.S. Provisional Patent Application Nos. 60/406,148,60/406,183, 60/406,184, 60/406,185, 60/406,234, and 60/406,254, all ofwhich were filed Aug. 26, 2002, and all are incorporated herein, intheir entirety, by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to vascular borders, or moreparticularly, to a system and method of using a first vascular image (orcontrol points located therein) to identify a border on a secondvascular image.

[0004] 2. Description of Related Art

[0005] The present invention relates to medical imaging arts. It findsparticular application to a system and method of identifying a border inan intra-vascular ultrasound (IVUS) image. It should be appreciated thatwhile the present invention is described in terms of identifying aluminal and medial-adventitial border on an IVUS image, the presentinvention is not so limited. Thus, for example, identifying any border(or boundary) in any vascular image is within the spirit and scope ofthe present invention.

[0006] Ultrasonic imaging of portions of a patient's body provides auseful tool in various areas of medical practice for determining thebest type and course of treatment. Imaging of the coronary vessels of apatient by ultrasonic techniques can provide physicians with valuableinformation. For example, the image data may show the extent of astenosis in a patient, reveal progression of disease, help determinewhether procedures such as angioplasty or atherectomy are indicated orwhether more invasive procedures may be warranted.

[0007] In a typical ultrasound imaging system, an ultrasonic transduceris attached to the end of a catheter that is carefully maneuveredthrough a patient's body to a point of interest such as within a bloodvessel. The transducer may be a single-element crystal or probe that ismechanically scanned or rotated back and forth to cover a sector over aselected angular range. Acoustic signals are then transmitted and echoes(or backscatter) from these acoustic signals are received. Thebackscatter data can be used to identify the type or density of ascanned tissue. As the probe is swept through the sector, many acousticlines are processed building up a sector-shaped image of the patient.After the data is collected, an image of the blood vessel (i.e., an IVUSimage) is reconstructed using well-known techniques. This image is thenvisually analyzed by a cardiologist to assess the vessel components andplaque content.

[0008] A typical analysis includes determining the size of the lumen andamount of plaque in the vessel. This is performed by generating an imageof the vessel (e.g., an IVUS image) and manually drawing contouredboundaries on the image where the clinician believes the luminal and themedial-adventitial borders are located. This is a very time consumingprocess. Furthermore, this process is made more difficult when multipleimages are being analyzed (e.g., to recreate a 3D vascular image, etc.)or the images are of poor quality (e.g., making the boundaries moredifficult to see). Thus, it would advantageous to have a system andmethod of identifying a border on a vascular image that overcomes atleast one of these drawbacks.

SUMMARY OF THE INVENTION

[0009] The present invention provides a system and method of using afirst vascular image, or more particularly a plurality of control pointslocated thereon, to identify a border on a second vascular image.Embodiments of the present invention operate in accordance with anintra-vascular ultrasound (IVUS) device and a computing deviceelectrically connected thereto. Specifically, in one embodiment of thepresent invention, an IVUS console is electrically connected to acomputing device and a transducer via a catheter. The transducer isinserted into a blood vessel of a patient and used to gather IVUS data(i.e., blood-vessel data, or data that can be used to identify the shapeof a blood vessel, its density, its composition, etc.). The IVUS data isthen provided to (or acquired by) the IVUS console, where it is used toproduce an IVUS image of the vessel.

[0010] The IVUS data (or multiple sets thereof) is then provided to (oracquired by) the computing device. In one embodiment of the presentinvention, the computing device includes a plurality of applicationsoperating thereon—i.e., a border-detection application, an extrapolationapplication, and an active-contour application. These applications areused to (i) identify a border and control points on a first IVUS image(i.e., any IVUS image), (ii) extrapolate the control points to a secondIVUS image (i.e., another IVUS image), (iii) identify a border on thesecond IVUS image, and (iv) adjust the border on the second IVUS imagein accordance with at least one factor.

[0011] Specifically, the border-detection application is adapted toidentify a border on a vascular image (e.g., an IVUS image). In oneembodiment of the present invention, this is accomplished by analyzingthe IVUS image, or IVUS data that corresponds to the IVUS image, todetermine certain gradients located therein. This is because borders ofvascular objects can be identified by a change in pixel color (e.g.,light-to-dark, dark-to-light, shade1-to-shade2, etc). Once the border isidentified, the border-detection application is used to identify atleast one control point (i.e., a starting-control point) on theidentified border. The extrapolation application is then used toidentify at least one control point (i.e., an additional control point)on at least one other IVUS image. In a preferred embodiment of thepresent invention, this is done by extrapolating the previouslyidentified control point (i.e., the starting-control point) to at leastone other IVUS image. Once the control point(s) is extrapolated, theextrapolating application is adapted to identify (or approximate) aborder that passes through the extrapolated point(s).

[0012] The active-contour application is then used to adjust theapproximated border (i.e., the border passing through the extrapolatedpoint(s)) to more closely match the actual border of the vascularobject. In doing so, the active-contour application may consider, ortake into account at least (i) image gradients (i.e., gradient factor),(ii) the proximity of the border to each extrapolated point (i.e.,continuity or control-point factor), and/or (iii) border curvature orsmoothness (i.e., curvature or boundary factor). Specifically, thegradient factor can be used to adjust the border if the neighboringpixels (as opposed to the pixels of the border) include bordercharacteristics (e.g., a dark-to-light transition, etc.). In otherwords, if the neighboring pixels include border-like characteristics (orat least more so than the pixels forming the border), then the border isadjusted. The continuity factor and the curvature factor can be used toensure that the border passes through each extrapolated point and doesnot include any sharp transitions (e.g., corners, etc.), respectively.In one embodiment of the present invention, the active-contourapplication is further adapted to adjust related borders on adjacentimages if the boarder is manually adjusted.

[0013] A more complete understanding of the system and method ofidentifying a border on an IVUS image will be afforded to those skilledin the art, as well as a realization of additional advantages andobjects thereof, by a consideration of the following detaileddescription of the preferred embodiment. Reference will be made to theappended sheets of drawings which will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 illustrates a vascular-border-identification system inaccordance with one embodiment of the present invention.

[0015]FIG. 2 illustrates and exemplary intra-vascular ultrasound (IVUS)image.

[0016]FIG. 3 illustrates a plurality of borders that can be identifiedin an IVUS image.

[0017]FIG. 4 illustrates a plurality of control points on one of theborders depicted in FIG. 3.

[0018]FIG. 5 illustrates how a plurality of 2D vascular images can beused to generate a 3D vascular image.

[0019]FIG. 6 illustrates how the control points from a first image(e.g., the image depicted in FIG. 4) can be extrapolated onto a secondimage.

[0020]FIG. 7 illustrates a vascular image including a luminal boundary,a medial-adventitial boundary, and a plaque component locatedtherebetween.

[0021]FIG. 8 illustrates a method of identifying a border of a vascularobject in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] The present invention provides a system and method of using afirst vascular image, or more particularly a plurality of control pointslocated thereon, to identify a border on a second vascular image. In thedetailed description that follows, like element numerals are used todescribe like elements illustrated in one or more figures.

[0023] Embodiments of the present invention operate in accordance withan intravascular ultrasound (IVUS) device and a computing deviceelectrically connected thereto. FIG. 1 illustrates avascular-border-identification system 10 in accordance with oneembodiment of the present invention. Specifically, an IVUS console 110is electrically connected to a computing device 120 and a transducer 114via a catheter 112. The transducer 114 is inserted into a blood vesselof a patient (not shown) and used to gather IVUS data (i.e.,blood-vessel data, or data that can be used to identify the shape of ablood vessel, its density, its composition, etc.). The IVUS data is thenprovided to (or acquired by) the IVUS console 110, where it is used toproduce an IVUS image of the vessel.

[0024] More particularly, IVUS data is typically gathered in segments,either through a rotating transducer or an array of circumferentiallypositioned transducers, where each segment represents an angular portionof an IVUS image. Thus, it takes a plurality of segments (or a set ofIVUS data) to image an entire cross-section of a vascular object.Furthermore, multiple sets of IVUS data are typically gathered frommultiple locations within a vascular object (e.g., by moving thetransducer linearly through the vessel). These multiple sets of data canthen be used to create a plurality of two-dimensional (2D) images or onethree-dimensional (3D) image. It should be appreciated that the presentinvention is not limited to the use of an IVUS device (or theacquisition of IVUS data), and may further include using thermographicdevices, optical devices (e.g., an optical coherence tomography (OCT)console), MRI devices, or any vascular imaging devices generally knownto those skilled in the art. It should further be appreciated that thecomputing device depicted in FIG. 1 includes, but its not limited to,personal computers or any other data-processing devices (general purposeor application specific) that are generally known to those skilled inthe art.

[0025] The IVUS data (or multiple sets thereof) is then provided to (oracquired by) the computing device 120. In one embodiment of the presentinvention, the computing device 120 includes a plurality of applicationsoperating thereon—i.e., a border-detection application 122, anextrapolation application 124, and an active-contour application 126.These applications are used to (i) identify a border and control pointson a first IVUS image (i.e., any IVUS image), (ii) extrapolate thecontrol points to a second IVUS image (i.e., another IVUS image), (iii)identify a border on the second IVUS image, and (iv) adjust the borderon the second IVUS image. It should be appreciated that the numberand/or location of the applications depicted in FIG. 1 are not intendedto limit the present invention, but are merely provided to illustratethe environment in which the present invention operates. Thus, forexample, using a single application to perform the applicationfunctions, as discussed herein, or remotely locating at least one of theapplications (in whole or in part) is within the spirit and scope of thepresent invention. It should further be appreciated that, while thepresent invention is discussed in terms of singularities (e.g.,identifying a border on one IVUS image, extrapolating control points toanother IVUS image, etc.), the present invention is not so limited. Infact, the present invention is particularly useful if it is used on aplurality of IVUS images (e.g., identifying borders on every fifth IVUSimage, extrapolating control points from the fifth IVUS image to thenext four IVUS images, etc.). It should also be appreciated that theterms “first” and “second,” as those terms are used herein, are usedbroadly to identify any two IVUS images. Thus, the phrase “second IVUSimage” may be used to identify an IVUS image distinct from a first IVUSimage (as opposed to the second IVUS image in a series of IVUS images).

[0026] Vascular objects include several identifiable borders. Forexample, the luminal border demarcates the blood-intima interface andthe medial-adventitial border demarcates the external elastic membrane(the boundary between the media and adventitia). By identifying theseborders, the plaque-media complex, which is located there between, canbe analyzed and/or calculated. It should be appreciated that the presentinvention is not limited to the identification of any particular border,and includes all vascular boundaries generally known to those skilled inthe art.

[0027] Referring back to FIG. 1, the border-detection application 122 isadapted to identify a border on a vascular image (e.g., an IVUS image).In one embodiment of the present invention, this is performed byanalyzing the IVUS image, or IVUS data that corresponds the IVUS image,to determine certain gradients located therein. This is because bordersof vascular objects can be identified by a change in pixel color (e.g.,light-to-dark, dark-to-light, shade 1-to-shade 2, etc).

[0028] For example, FIG. 2 illustrates an exemplary IVUS image 20 of avascular object. Starting from the center and working outward, thecatheter can be identified by the first light-to-dark transition (orgradient). The catheter border is further identified in FIG. 3 (i.e.,330). Referring back to FIG. 2, and continuing outward, the nextdark-to-light transition (or gradient) identifies the luminal border(i.e., see FIG. 3, 320). The medial-adventitial border can then beidentified by going outward from the luminal border until the nextdark-to-light transition (or gradient) is found (see FIG. 3, 310). Itshould be appreciated that because the IVUS image is constructed usinggray-scales, it may be necessary to utilize an algorithm and/or at leastone threshold value to identify precisely where the image changes fromlight to dark (or vice versa). However, it should further be appreciatedthat the present invention is not limited to any particular algorithmfor identifying the aforementioned transitions, and includes allalgorithms (and/or threshold values) generally known to those skilled inthe art.

[0029] Once the border is identified, the border-detection algorithm isfurther adapted to identify at least one control point on the border.For example, with reference to FIGS. 3 and 4, the border-detectionalgorithm can be used to identify a plurality of control points 22 onthe luminal border 320. It should be appreciated that the location andnumber of control points depicted in FIG. 4 are not intended to limitthe present invention, and are merely provided to illustrate theenvironment in which the present invention may operate. In an alternateembodiment, the border-detection application 122 is adapted to identifya border using user-identified control points. Such an embodiment isdiscussed in detail in U.S. Pat. No. 6,381,350, which issued Apr. 30,2002, and is incorporated herein, in its entirety, by reference.

[0030] Referring back to FIG. 1, once the border and control point(s)are identified on a first vascular image, the extrapolation application124 is used to identify at least one control point on at least one otherIVUS image. In a preferred embodiment of the present invention, this isdone by extrapolating the previously identified control points to atleast one other IVUS image. By doing this, multiple 2D images (or atleast one 3D image) can be produced. For example, as illustrated in FIG.5, multiple 2D images (e.g., 20, 52 a-52 d, etc.) are used to produce a3D image of a tubular (e.g., vascular) object 50.

[0031]FIG. 6 illustrates how an identified control point can beextrapolated to another IVUS image. Specifically, the control pointsthat were illustrated in FIG. 4 (i.e., 22) are extrapolated (or copied)to another IVUS image (e.g., 52 d), thus creating a second set ofcontrol points 62. In one embodiment of the present invention, thecontrol points are extrapolated using Cartesian coordinates. It shouldbe appreciated that, while FIG. 6 illustrates control points beingextrapolated to an adjacent image, the present invention is not solimited. Thus, extracting control points to additional images (e.g., 52c, 52 b, etc.) is within the spirit and scope of the present invention.

[0032] Once the control points are extrapolated, the extrapolatingapplication is further adapted to identify (or approximate) a borderbased on the extrapolated points. For example, as shown in FIG. 6, theextrapolated points 62 may be connected using a plurality of lines 64,where the lines are either straight or curved (not shown). In anotherembodiment of the present invention, the extrapolating application isadapted to use an algorithm (e.g., a cubic-interpolation algorithm,etc.) to identify line shape.

[0033] Referring back to FIG. 1, the active-contour application 126 isthen used to adjust the border to more closely match the actual borderof the vascular object. In doing so, the active-contour application 126may consider or take into account at least (i) image gradients (i.e.,gradient data), (ii) the proximity of the border to each extrapolatedpoint (i.e., continuity or control-point factor), and/or (iii) bordercurvature or smoothness (i.e., curvature or boundary factor).Specifically, by considering gradient data (or a gradient factor), theborder can be adjusted if the neighboring pixels (as opposed to thepixels of the border) include border characteristics (e.g., adark-to-light transition, etc.). By considering a continuity orcontrol-point factor, the border can be adjusted so that it passesthrough each extrapolated point. Furthermore, by considering a curvatureor boundary factor, the border can be adjusted to prevent sharptransitions (e.g., corners, etc.). In one embodiment of the presentinvention, the continuity and curvature factors are also used to connectrelated borders on adjacent images. It should be appreciated that ifmultiple factors are being considered, then individual factors may beweighted more heavily than others. This becomes important if the factorsproduce different results (e.g., the gradient factor suggests adjustingthe border away from an extrapolated point, etc.). It should further beappreciated that the active-contour application may also be used toadjust the border identified by the border-detection application. Itshould also be appreciated that the present invention is not limited tothe use of the aforementioned factors for border optimization, and thatthe use of additional factors (e.g., frequency factor, etc.) to adjust(or optimize) a border is within the spirit and scope of the presentinvention.

[0034] In one embodiment of the present invention, the adjusted bordersare configured to be manually manipulated. In other words, at least onepoint on the border can be selected and manually moved to a newlocation. The active-contour application is then used (as previouslydiscussed) to reconstruct the border accordingly. In another embodimentof the present invention, the active-contour application is furtheradapted to adjust related borders in adjacent images. This is done byfitting a geometrical model (e.g., a tensor product B-spline, etc.) overthe surface of a plurality of related borders (e.g., as identified onmultiple IVUS images). A plurality of points on the geometrical modelare then parameterized and formulated into a constrained least-squaressystem of equations. If a point on the border is manually moved, theactive-contour application can utilize these equations to calculate aresulting surface (or mesh of control points). The affected borders(e.g., adjacent borders) can then be adjusted accordingly.

[0035] Once the border has been sufficiently adjusted, theaforementioned process can be repeated to identify additional borders.In an alternate embodiment of the present invention, multiple borders(e.g., luminal and medial-adventitial borders) are identifiedconcurrently. The multiple border can then be imaged (in either 2D or3D) and analyzed by either a skilled practitioner or a computeralgorithm. For example, as illustrated in FIG. 7, the luminal border 74and the medial-adventitial border 76 can be used (by either a clinicianor an algorithm) to identify the plaque-media complex 78 of a vascularobject.

[0036] One method of identify a border on a vascular image isillustrated in FIG. 8. Specifically, in step 810, multiple sets of IVUSdata are acquired, where each set of IVUS data corresponds to a 2D IVUSimage. At step 812, a border is approximated in one IVUS image (e.g.,using gradient data, etc.). Control points on the approximated borderare then identified at step 814. At step 816, these control points arethen used to identify additional control points on additional 2D IVUSimages (e.g., via extrapolation, etc.). These additional control pointsare then used to approximate at least one other border at step 818,which is then adjusted at step 820. In one embodiment, the border isadjusted in accordance with at least gradient data.

[0037] Having thus described a preferred embodiment of a system andmethod of identifying a border on a vascular image, it should beapparent to those skilled in the art that certain advantages of thesystem have been achieved. It should also be appreciated that variousmodifications, adaptations, and alternative embodiments thereof may bemade within the scope and spirit of the present invention. The inventionis further defined by the following claims.

What is claimed is:
 1. A method of identifying a border of a vascularobject, comprising: acquiring multiple sets of blood-vessel data, eachset corresponding to an image of a vascular object; using a set ofblood-vessel data to approximate a border on an image of said vascularobject; identifying at least one control point on said border;extrapolating said at least one control point to at least one other setof blood-vessel data, creating at least one other control point on atleast one other image; using said at least one other control point toapproximate at least one other border on said at least one other image;and adjusting said at least one other border in accordance with at leasta gradient factor.
 2. The method of claim 1, wherein said step ofacquiring multiple sets of blood-vessel data further comprises acquiringmultiple sets of intra-vascular ultrasound (IVUS) data, where each setcorresponds to an IVUS image of said vascular object.
 3. The method ofclaim 1, wherein said step of using a set of blood-vessel data toapproximate a border further comprises identifying gradients in saidimage and using said gradients to approximate said border on said imageof said vascular object.
 4. The method of claim 1, wherein said step ofextrapolating said at least one control point further comprisesextrapolating said at least one control point to an adjacent set ofblood-vessel data, said adjacent set corresponding to another imageadjacent to said image.
 5. The method of claim 1, wherein said stepadjusting said at least one other border further comprises adjustingsaid at least one other border in accordance with at least a continuityfactor, said continuity factor representing an amount of continuitybetween adjacent control points on said at least one other border. 6.The method of claim 1, wherein said step of adjusting said at least oneother border further comprises adjusting said at least one other borderin accordance with at least a curvature factor, said curvature factorrepresenting an amount of continuity between adjacent portions of saidat least one other border.
 7. The method of claim 5, wherein said stepof adjusting said at least one other border further comprises adjustingsaid at least one other border in accordance with at least a curvaturefactor, said curvature factor representing an amount of continuitybetween adjacent portions of said at least one other border.
 8. Themethod of claim 4, further comprising automatically adjusting anadjacent border if said border is manually adjusted, said adjacentborder being located on said another image.
 9. A border-identificationsystem comprising: a computing device adapted to be electricallyconnected to a data-gathering device and to acquire from saiddata-gathering device multiple sets of blood-vessel data, each setcorresponding to an image of a vascular object; a border-detectionapplication operating on said computing device and adapted to use atleast a portion of said blood-vessel data to produce starting-borderdata and starting-control-point data, said starting-border datarepresenting at least one border on at least one image of said vascularobject and said starting-control-point data representing at least onecontrol point on said at least one border; an extrapolation applicationoperating on said computing device and adapted to use saidstarting-control-point data to produce additional-control-point data andadditional-border data, said additional-control-point data representingat least one other control point on at least one other image and saidadditional-border data representing at least one other border on said atleast one other image; and an active-contour application operating onsaid computing device and adapted to adjust said at least one otherborder.
 10. The border-identification system of claim 9, wherein saiddata-gathering device comprises an intra-vascular ultrasound (IVUS)console.
 11. The border-identification system of claim 9, wherein saidborder-detection application is further adapted to identify gradients insaid at least one image and use said gradients to producestarting-border data.
 12. The border-identification system of claim 11,wherein said border-detection application is further adapted to use saidstarting-border data to produce said starting-control-point data. 13.The border-identification system of claim 9, wherein said extrapolationapplication is further adapted to produce said additional-border data byusing cubic interpolation to connect adjacent ones of said at least oneother control point.
 14. The border-identification system of claim 9,wherein said active-contour application is further adapted to usegradient data to adjust said at least one other border, said gradientdata representing gradients in said at least one other image.
 15. Theborder-identification system of claim 14, wherein said active-contourapplication is further adapted to consider the continuity of adjacentones of said at least one other control point in adjusting said at leastone other border.
 16. The border-identification system of claim 15,wherein said active-contour application is further adapted to considerthe curvature of said at least one other border in adjusting said atleast one other border.
 17. The border-identification system of claim 9,wherein said active-contour application is further adapted to adjustsaid at least one other border in accordance with at least one factor,said at least one factor being selected from the group consisting of agradient factor, a continuity factor and a curvature factor.
 18. Amethod of identifying a boundary on an intra-vascular ultrasound (IVUS)image, comprising: using a plurality of control points on a first IVUSimage to identify additional control points on a second IVUS image;using said additional control points to identify a boundary on saidsecond IVUS image; adjusting said boundary in accordance with at leastone factor, said at least one factor being selected from a groupconsisting of gradient factor, control-point factor and boundary factor,where said control-point factor corresponds to the connectivity ofadjacent ones of said additional control points and said boundary factorcorresponds to the curvature of said boundary.
 19. The method of claim18, further comprising using at least a portion of first IVUS data toidentify said plurality of control points, said first IVUS datacorresponding to said first IVUS image.
 20. The method of claim 18,wherein said step of using a plurality of control points on a first IVUSimage to identify additional control points on a second IVUS imagefurther comprises extrapolating said plurality of control points on saidsecond IVUS image.